Just a question to all of you out there. I was wondering how many of you have remover the secondary air filter, and also did it do any good for you, maybe something bad happened because of it. What about the gas milage did it improve or get worse. I'm mainly concerned if buy removing the filter anything bad happened. All responses are welcome, and thanks in advace.

i removed the sec. air filter on my 06 prerunner with the 4.0 v6, and it didnt make that much of a difference as far as mileage, maybe throttle response is a tad better, and it definitely made it a little louder also(well, i have an airaid intake too). 007tacoma(mark) did a write up about it, and his is a 4 banger,and he and others with the 4banger say there is a big difference by removing the sec filter.

I'll confirm the slightly better throttle response, and I add to that about a half mile per gallon improvement in fuel mileage. (I was obsessively tracking my mileage in preperation for the ECO System test when I did it.) 4.0L v6 6 speed manual 4x4 access cab.

The secondary filter is there to absorb hydrocarbons from any unburned fuel from escaping out of the engine thru the airbox and into the atmosphere when the engine is turned off.

IMHO It won't have any effect on exhaust emmissions because

a) Unless you were running the truck in a NBC like contaminated area there is nothing a carbon filter could do to change what exits the tail pipe.

b) The airflow into the running engine is too great for such a thin layer of charcoal to have time to remove anything harmful. That would take a complex (and extreemly restrictive) filteration system, something like a giant paint respirator which would have to be changed after a set number of hours of operation.

Based on that link, it really makes me wonder why the filter is in-line all the time. Seems to me it would make more sense to have some sort of valve to direct air through it or not just based upon when it's needed, which seems to be while the engine is off (to capture emissions) and the first couple of minutes of running (to emit captured emissions into engine for burning). After that, switch it out of the airflow with some sort of valve so you have a better breathing engine.

I just realized I never answered the original question. Sorry about that.

I had posted on that other thread when I removed secondary filter that I noticed better throttle response and the truck has an easier time maintaining speed climbing hills on cruise control.

I am obsessive about tracking my gas use and compared the average of the two tanks used before removing the secondary filter to the two tanks used after removal. It gave me an increase of about .9 mpg.

No negative side effects after about 1000 miles. Since these engines did not have that filter in the years before 2005 I don't expect any. Some people mention their truck sounds louder after removing the filter but I didn't notice any real change in the sound.

wow guys thanks for all the responses greatly apreciated. so i'm about to go to take that filter off cant wait to see what happens. buy the way for those of you that wanted to know where i live, i'm in IL. thanks again

Based on that link, it really makes me wonder why the filter is in-line all the time. Seems to me it would make more sense to have some sort of valve to direct air through it or not just based upon when it's needed, which seems to be while the engine is off (to capture emissions) and the first couple of minutes of running (to emit captured emissions into engine for burning). After that, switch it out of the airflow with some sort of valve so you have a better breathing engine.

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This would not only be expensive as mentioned, but more moving parts that would either need servicing or they would have operating problems as they got older. I know on my 7.3l Ford Diesel I removed the exhaust back pressure valve out of the turbine housing because it does fail and you won't know it until it gets horrible mileage or a loss in power and its a pita to deal with because you have to take the turbo off.

I started to drill mine out tonight. Got to looking and it seems that removing it with even the AFE oil free drop in, made out of rubber on the edges, there would be some slop in the fit allowing stuff to bypass the filter into the engine. Those that have removed the secondary have you just cut it out leaving the outer edge or what has been used as a spacer? Thanks

I removed the secondary filter intact and could reinstall it if needed for some reason in the future. If you look at the airbox assembly the secondary filter is nowhere close to the drop in filter and won't have any effect on how well closing the airbox seals the drop in's edges